SDS-PAGE are gels that are used to separate proteins by their masses. SDS, or sodium dodecyl sulfate, is a detergent that denatures the protein to its primary structure. PAGE stands for polyacrylamide gel electrophoresis. This separates the proteins by their charge because most of the proteins are positively charged in the gel due to a higher pH. This allows them to move toward an positive electrode and separate the proteins by mass in the SDS-PAGE gel.